A sensitive, quantitative assay is being developed to study the biologic effects of the DNA viral intermediate and provirus of mammalian C-type RNA viruses. This procedure will be used to assess the ability of DNA to be infectious and/or to induce cellular transformation. Optimal conditions for extraction and titration of viral-specific DNA are being defined. The effect of chemical and physical treatment on virus expression will be evaluated. Differences between unexpressed and expressed endogenous and exogenous viral genomes are under study. Preliminary results indicate that DNA from AKR mouse cells (which contain endogenous viral genomes) can be rendered infectious when cells are treated with 5-iododeoxyuridine prior to extraction of DNA, while DNA from untreated cells is not infectious. The physical changes in DNA which underly these biologic differences are being explored.